8/27/03
OPTICALLY ISOLATED
ERROR AMPLIFIER
Page 1 of 13
FOD2742A
FOD2742B
FOD2742C
2003 Fairchild Semiconductor Corporation
DESCRIPTION
The FOD2742 Optically Isolated Amplifier consists of the popular KA431 precision
programmable shunt reference and an optocoupler. The optocoupler is a gallium arsenide
(GaAs) light emitting diode optically coupled to a silicon phototransistor. It comes in 3
grades of reference voltage tolerance = 2%, 1%, and 0.5%.
The Current Transfer Ratio (CTR) ranges from 100% to 200%. It also has an outstanding
temperature coefficient of 50 ppm/C. It is primarily intended for use as the error amplifier/
reference voltage/optocoupler function in isolated ac to dc power supplies and dc/dc con-
verters.
When using the FOD2742, power supply designers can reduce the component count and
save space in tightly packaged designs. The tight tolerance reference eliminates the need
for adjustments in many applications. The device comes in a 8-pin small outline package.
FEATURES
Optocoupler, precision reference and error amplifier in single package
2.5V reference
CTR 100% to 200%
2,500V RMS isolation
UL approval E90700, Volume 2
BSI approval 8661, 8662
VDE approval 136616
CSA approval 1113643
Low temperature coefficient 50 ppm/C max
FOD2742A: tolerance 0.5%
FOD2742B: tolerance 1%
FOD2742C: tolerance 2%
APPLICATIONS
Power supplies regulation
DC to DC converters
* The compensation network must be attached between pins 6 and 7.
PIN DEFINITIONS
Pin Number
Pin Name
Pin function description
1
NC
Not connected
2
C
Phototransistor Collector
3
E
Phototransistor Emitter
4
NC
Not connected
5
GND
Ground
6
COMP
Error Amplifier Compensation. This pin is the output of the error amplifier. *
7
FB
Voltage Feedback. This pin is the inverting input to the error amplifier
8
LED
Anode LED. This pin is the input to the light emitting diode.
FUNCTIONAL BLOCK DIAGRAM
1
2
3
4
5
6
7
8 LED
FB
COMP
GND
NC
C
E
NC
8/27/03
Page 2 of 13
2003 Fairchild Semiconductor Corporation
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2742A
FOD2742B
FOD2742C
TYPICAL APPLICATION
V
O
V
1
R1
R2
2
3
8
6
7
5
PWM
Control
FAN4803
FOD2742
Notes
1. Derate linearly from 25C at a rate of 2.42 mW/ C
2. Derate linearly from 25C at a rate of 1.42 mW/ C.
3. Derate linearly from 25C at a rate of 2.42 mW/ C.
4. Functional operation under these conditions is not implied. Permanent damage may occur if the device is subjected to conditions
outside these ratings.
ABSOLUTE MAXIMUM RATINGS
(T
A
= 25C Unless otherwise specified.)
Parameter
Symbol
Value
Units
Storage Temperature
T
STG
-40 to +125
C
Operating Temperature
T
OPR
-25 to +85
C
Reflow Temperature Profile (refer to fig. 21)
Input Voltage
V
LED
37
V
Input DC Current
I
LED
20
mA
Collector-Emitter Voltage
V
CEO
70
V
Emitter-Collector Voltage
V
ECO
7
V
Collector Current
I
C
50
mA
Input Power Dissipation (note 1)
PD1
145
mW
Transistor Power Dissipation (note 2)
PD2
85
mW
Total Power Dissipation (note 3)
PD3
145
mW
8/27/03
Page 3 of 13
2003 Fairchild Semiconductor Corporation
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2742A
FOD2742B
FOD2742C
1. The deviation parameters V
REF(DEV)
and I
REF(DEV)
are defined as the differences between the maximum and minimum values
obtained over the rated temperature range. The average full-range temperature coefficient of the reference input voltage,
V
REF
,
is defined as:
where
T
A
is the rated operating free-air temperature range of the device.
2. The dynamic impedance is defined as |Z
OUT
| =
V
COMP
/
I
LED
. When the device is operating with two external resistors
(see Figure 2), the total dynamic impedance of the circuit is given by:
ELECTRICAL CHARACTERISTICS
(T
A
= 25C Unless otherwise specified.)
INPUT CHARACTERISTICS
Parameter
Test Conditions
Symbol
Device
Min.
Typ.
Max.
Unit
LED Forward Voltage
(I
LED
= 10 mA, V
COMP
= V
FB
) (fig. 1)
V
F
ALL
1.20
1.5
V
Reference Voltage
I
LED
= 10 mA, V
COMP
= V
FB
(fig. 1)
V
REF
A
2.482
2.495
2.508
V
B
2.470
2.495
2.520
V
C
2.450
2.500
2.550
V
Deviation of V
REF
over
temperature
T
A
= -25C to +85C (fig. 1) V
REF (DEV)
ALL
3.5
17
mV
Ratio of V
REF
variation to the
output of the error amplifier
I
LED
= 10 mA
(fig. 2)
V
COMP
= 10V to V
REF
V
REF
/
V
COMP
ALL
-0.5
-2.7
mV/
V
V
COMP
= 36V to 10V
-0.3
-2.0
Feedback Input Current
I
LED
= 10mA, R
1
= 10K
(fig. 3)
I
REF
ALL
2.2
4
A
Deviation of I
REF
over
temperature
T
A
= -25C to +85C (fig. 3)
I
REF (DEV)
ALL
1.0
1.2
A
Minimum Drive Current
V
COMP
= V
FB
(fig. 1)
I
LED (MIN)
ALL
0.45
1.0
mA
Off-state error amplifier current
V
LED
= 37V, V
FB
= 0 (fig. 4)
I
(OFF)
ALL
0.01
1.0
A
Error amplifier output impedance
(see note 2)
V
COMP
= V
REF
, I
LED
= 1mA to 20mA,
f
1.0 kHz
|Z
OUT
|
ALL
0.15
0.5
V
REF
ppm/C
(
)
V
REF DEV
(
)
/V
REF
T
A
25C
=
(
)
{
} 10
6
T
A
-----------------------------------------------------------------------------------------------------
=
Z
OUT, TOT
=
V
I
--------
Z
OUT
1
R1
R2
--------
+
8/27/03
Page 4 of 13
2003 Fairchild Semiconductor Corporation
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2742A
FOD2742B
FOD2742C
Notes
1. Device is considered as a two terminal device: Pins 1,2 3 and 4 are shorted together and Pins 5,6,7 and 8 are shorted together.
2. Common mode transient immunity at output high is the maximum tolerable (positive) dVcm/dt on the leading edge of the
common mode impulse signal, Vcm, to assure that the output will remain high. Common mode transient immunity at output
low is the maximum tolerable (negative) dVcm/dt on the trailing edge of the common pulse signal,Vcm, to assure that the
output will remain low.
OUTPUT CHARACTERISTICS
(T
A
= 25C Unless otherwise specified.)
Parameter
Test Conditions
Symbol
Min
Typ
Max
Unit
Collector dark current
(V
CE
= 10 V) (Fig. 5)
I
CEO
1
50
nA
Emitter-collector voltage breakdown
(I
E
= 100 A)
BV
ECO
7
10
V
Collector-emitter voltage breakdown
(I
C
= 1.0mA)
BV
CEO
70
120
V
TRANSFER CHARACTERISTICS
(T
A
= 25C Unless otherwise specified.)
Parameter
Test Conditions
Symbol
Min
Typ
Max
Unit
Current transfer ratio
(I
LED
= 10 mA, V
COMP
= V
FB
,
V
CE
= 5 V) (Fig. 6)
CTR
100
140
200
%
Collector-emitter
saturation voltage
(I
LED
= 10 mA, V
COMP
= V
FB,
I
C
= 2.5 mA) (Fig. 6)
V
CE
(SAT)
0.16
0.4
V
ISOLATION CHARACTERISTICS
(T
A
= 25C Unless otherwise specified.)
Parameter
Test Conditions
Symbol
Min
Typ
Max
Unit
Input-output insulation
leakage current
(RH = 45%, T
A
= 25C, t = 5s,
V
I-O
= 3000 VDC) (note. 1)
I
I-O
1.0
A
Withstand insulation
voltage
(RH <= 50%, T
A
= 25C, t = 1 min)
(note 1)
V
ISO
2500
Vrms
Resistance (input to output)
V
I-O
= 500 VDC (note 1)
R
I-O
10
12
Ohm
SWITCHING CHARACTERISTICS
(T
A
= 25C Unless otherwise specified.)
Parameter
Test Conditions
Symbol
Min
Typ
Max
Unit
Bandwidth
(Fig. 7)
BW
10
kHZ
Common mode transient
immunity at output high
(I
LED
= 0 mA,
Vcm = 10 V
PP
RL = 2.2 kV (Fig. 8) (note 2)
CMH
1.0
kV/s
Common mode transient
immunity at output low
(I
LED
= 10 mA,
Vcm = 10 V
PP
RL = 2.2 kV (Fig. 8) (note 2)
CML
1.0
kV/s
8/27/03
Page 5 of 13
2003 Fairchild Semiconductor Corporation
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2742A
FOD2742B
FOD2742C
I
(LED)
V
(LED)
V
COMP
V
COMP
I
CEO
V
CE
V
REF
V
CE
I
(LED)
V
F
V
REF
V
REF
8
2
3
2
3
V
V
V
6
7
5
I
(LED)
I
(LED)
I
(C)
I
(OFF)
I
REF
8
6
2
3
2
3
2
3
V
V
7
5
8
6
7
5
8
6
7
5
8
6
2
3
7
5
R1
8
6
R1
R2
7
5
FIG. 1. V
REF
, V
F,
I
LED
(min) TEST CIRCUIT
FIG. 3. I
REF
TEST CIRCUIT
FIG. 5. I
CEO
TEST CIRCUIT
FIG. 6. CTR, V
CE(sat)
TEST CIRCUIT
FIG. 4. I
(OFF)
TEST CIRCUIT
FIG. 2.
V
REF/
V
COMP
TEST CIRCUIT
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